As is well known, due to increases in oil prices and exhaust gas regulations, eco-friendly policies and fuel efficiency improvement have been researched in vehicle development. Accordingly, vehicle manufacturers have developed a technology for reducing fuel consumption and decreasing exhaust gas to meet eco-friendly policies and improve fuel efficiency.
Additionally, vehicle manufacturers have focused efforts in developing a technology of a hybrid vehicle which efficiently combines and uses power of an engine and a motor to achieve high fuel efficiency. Hybrid vehicles have met purchase demands of many customers by virtue of high fuel efficiency and eco-friendly characteristics.
FIG. 1 illustrates an exemplary configuration of a typical hybrid vehicle.
Referring to FIG. 1, the hybrid vehicle may include an engine 10, a drive motor 20, an engine clutch 30 for combining or releasing power between the engine 10 and the drive motor 20, a transmission 40, a differential gear device 50, a battery 60, a starting/generating motor 70 for starting the engine 10 or generating power by torque of the engine 10, and a plurality of wheels 80.
Further, the hybrid vehicle may include a hybrid controller (HC) 100 for controlling all operations of the hybrid vehicle and a battery controller (BC) 160 for managing and controlling the battery 60. The battery controller 160 may be referred to as a battery management system (BMS).
The constituent elements of a conventional hybrid vehicle are known to those skilled in the art, and thus, a more detailed description will be omitted.
The starting/generating motor 70 may be called an integrated starter and generator (ISG) or hybrid starter and generator (HSG), in the known art. Hereinafter, in the present specification, the starting/generating motor 70 may be referred to as a starting motor.
The hybrid vehicle may run in a driving mode, such as an electric vehicle (EV) mode using only torque of the drive motor 20, a hybrid electric vehicle (HEV) mode using torque of the drive motor 20 as an auxiliary power source while using torque of the engine 10 as a main power source, and a regenerative braking (RB) mode during braking or when the vehicle runs by inertia. In the RB mode, braking and inertia energies are collected through the electric power generation of the drive motor 20, and the battery 60 is charged with the collected energy.
As described above, the hybrid vehicle uses both mechanical energy of the engine and electrical energy of the battery. The hybrid vehicle uses an optimum operation region of the engine and the drive motor and collects the energy by the drive motor while braking, thereby improving fuel efficiency and efficiently using the energy.
In the hybrid vehicle, a running method may be generally divided according to a state of charge (SOC) of the battery 60.
FIG. 2 is an exemplary diagram illustrating an SOC of the battery 60 according to a running method of the hybrid vehicle.
Referring to FIG. 2, the charge of the battery 60 of the hybrid vehicle may be divided into a critical overcharge region CH (critical high), an overcharge region H (high), a normal charge region N (normal), a low charge region L (low), and a critical low charge region CL (critical low) according to the SOC. The low charge region may be divided approximately in half to be two regions L1 and L2.
The BC 160 of the hybrid vehicle may perform part load charge control, idle charge control, and power limit control to maintain the SOC of the battery 60 as illustrated in FIG. 2.
Based on the contents illustrated in FIG. 2, the part load charge control is generally performed when the SOC of the battery is in the normal charge region N. The idle charge control is generally performed when the SOC of the battery is in the upper low charge region L1. The power limit control is generally performed when the SOC of the battery is in the lower low charge region L2 and the critical low charge region CL.
While the power limit control is performed, power that is used by an electrical equipment of a high voltage power module system may be limited.
Accordingly, while the power limit control is performed, when an EV running mode needs to be changed into an HEV running mode in a situation in which speed of the drive motor 20 is high, the battery power has to be used first to start the engine. In this case, since power to drive the drive motor may become lacking, drivability and acceleration performance may deteriorate.
In other words, in the prior art, when the battery is in a discharge limit state, such as when the SOC is low, the drive motor is being driven, and a change to the HEV running mode in which the starting motor has to be driven to start the engine is requested, since a portion of available power of the battery should be used to drive the starting motor for starting the engine as illustrated in FIG. 3, problems associated with acceleration performance may occur while the engine clutch is engaged.
The above information disclosed in this section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.